CPSC 2150 - DAY 2
AUGUST 23, 2016

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Primitive/Reference Types and Value Semantics
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Java contains 8 primitive types
	.boolean
	.byte
	.short
	.int
	.long
	.float
	.double
	.char

Variable Declaration (Not automatically initialized if local variables)

short index;
boolean isDone = true;
int counter = 3;
float tip = cost * 0.15;

Char vs. Short (char is signed, short is unsigned)

When writing a long constant, use an upper case L

long x = 13L;

lowercase syntactically correct, but confusing

For consistency prefer F to f.

Every int is long, so long is a bigger type

Heirarchy

	Double
	  |
	Float
	  |
	long
	  |
       	int 
	  |    \
	short   char
	  |
	byte

Widening is automatic when needed (i.e. implicit)

int i = 13; 	//no type conversion
long x = 12;	//int to long (widening)
long y = i;	//int to long (widening)

Widening can be forced by an explicit cast

int sum = 76;
int count = 10;

float average = sum/count;
	// no widening
average = sum/(float)count;
	//int to float widening, result is 7.6


Narrowing requires EXPLICIT CAST

Cast is a promise by program that the narrowing type conversion is ok

May result in loss of information
	.casting float to int truncates decimals
	.casting long to int discards top bytes

Assignment is a copy

Parameters are copied

Class types provided by:
	. Java standard libraries
		.string, integer, date, system
	.Programmer
		.Person, animal, savings, helloworldapp

	.Arrays
		.can contain primitive or reference types
			.int[], float[], String[]
		.indexed starting from 0
	.just one literal null

For reference types, the "value" in the memory location is a pointer to the
actual object.

Declaration binds the variable to a memory location which contains a pointer

Explicit object creation with new()

java.util.Date d = new java.util.Date();

Using Arrays
------------

An array type does not include the length
int[] ids = new int[rostersize];
int searchRoster(int[] students) {...}

Array Length 
Set at run time, cannot change after initialization.
Avaliable as a property with .length

Iteration: "foreach" loop (keyword is for)

int sum = 0;
for(int a: ids)
	sum+=a;
float average = sum/(float)ids.length

Set in Stone - can't change the size after initialized

Assignment creates and Alias
----------------------------

Assignment copies the pointer

accountB - $300 -| Points to same pointer, if you change one, it changes
accountA - $300 -| the other

accountB.deposit(150);

accountB - $450 -| Same account balance because same 
accountA - $450 -| pointer, when deposit is made.

For references p,q consider p == q
	.compares pointers for equality!
	.do they refer to the same object???

	p = 0xFF (contains 4)
	q = 0xFF (contains 4)  

	THEY ARE SAME POINTER SO THEY ARE EQUAL

To test for equalty

	P = 0xAF (contains 4)
	Q = 0xFF (contains 4)

	.equals will return value, comparison can be made there

Immutable Wrapper Classes
-------------------------

Every primitive type has a corresponding wrapper class
	.int, long, float, double

The classes are immutable
	.so no aliasing worries

Do not provide a zero-argument constructor
Do provide useful static constants
	Integer.MAX_VALUE, Integer.MIN_VALUE

Do provide useful static methods
	Converting from string to primitive